The invention refers to a surface rewinding machine-and method for the formation of logs or rolls of web material wound on a central core. Such rewinding machines are well-known, described, for example, in U.S. Pat. Nos. 4,487,377; 4,723,724; 4,327,877 and 4,828,195; U.K. Patent No. 2,105,688; and in EP-A-0 498 039.
More in particular, the present invention refers to a rewinding machine which includes a first winder roller on which the web material is fed; a second winder roller defining, with the first winder roller, a nip through which the care and the web material pass; means for feeding the web material to the nip; means for introducing a core on which the web material is to be wound; and a web material severing means cooperating with the first winder roller.
A rewinder of this type is described, for example, in U.S. Pat. No. 4,487,377.
These rewinders are used for producing smaller diameter logs or rolls of web material from large diameter parent rolls. Typically, these machines are used in the paper converting industry to produce rolls of toilet paper, kitchen towels, all-purpose wipers and the like. The formed logs may be as long as 350 cm and only 10-15 cm in outer diameter, and are subsequently cut transversely to their axis to obtain small rolls which may be only 10-30 cm long.
In the production of such logs, it is important to use reliable machines able to run at high production speeds (in the range of 600-1000 m/minute) which provide a consistently high-quality product, with uniform windings, especially of the first loops. The length of the material on each log must be presettable and maintained, from log-to-log, with great accuracy.
One way to obtain high production rates and a high quality of the manufactured product is shown in U.S. Pat. No. 4,487,377, which provides for a web-cutting member which cooperates with the first winder roller of the rewinder. The web material is cut upstream of the point where the core is introduced. After cutting, the leading edge of the web material adheres to the surface of the winder roller and is transferred (by the rotation of the latter) towards the winding region where the leading edge is made to adhere to a new core suitably introduced by an insertion means.
This machine requires means (for holding the leading edge of the web material onto the winder roller) which are housed inside the winder roller and which must be timely activated and deactivated to hold and release the edge at preset moments, thereby allowing the starting of the winding on a new core.
In U.S. Pat. No. 4,327,877 a machine is described, wherein the web is torn between the core and the second winding roller once the core has been introduced into the nip. Tearing is obtained by a suction means inside the second winding roller. The suction means forms a loop of web material which is pinced between the new core and the second roller.
A first object of the present invention is a rewinding machine which is able to produce a high quality finished product at high speeds with a simpler and more economical construction than that of known rewinders. A further object of the present invention is to provide a versatile rewinder able to produce logs of varying length without requiring complex mechanisms for adaptation to different lengths of web material without a slipping of the web material on the winder roller onto which it is fed. Another object of the present invention is the construction of a rewinder having means for tearing or cutting the web material, which means are reliable, simple, and inexpensive to produce and maintain.
These and further objects and advantages will appear evident to the skilled in the art by the following description.
In the rewinder according to the present invention, a surface or track is provided upstream of the nip between the winder rollers, which defines, together with the web feeding means which feeds the web material into the nip, a channel into which the core is introduced. A web severing means cooperates with the web feeding means at an intermediate position along the channel between the region of insertion of the new core and the nip defined between the winder rollers.
According to the invention, a machine is provided wherein a core is inserted into a channel upstream of the nip between a first and a second winder roller. The web material is severed downstream of the core insertion region by severing means which cooperate with the first winder roller or other means for feeding the material into the nip. This avoids the need of accelerating one of the winder rollers, and the severed web material begins to wind up on the core while the core starts to roll into the channel and on the surface or track by the rotation of the first winder roller. In some cases, the web-feeding means may be a belt system combined with the first winder roller.
This arrangement allows a precise severance of the web material to be carried out by severing means which cooperate with the first winder roller, without having to hold the leading edge of the web material on the winder roller, inasmuch as at the moment of severance of the web material, the new core is already in contact with the web material. Furthermore, the un-tensioning of the web material upstream of the winding region is substantially eliminated.
If desired, the start of the winding of the web material around the core may be assisted by placing glue on the surface of the core, or by suitable air jet or vacuum or mechanical means. The use of glue ensures a more reliable operation and increases the quality of the final product.
The surface or track for the rolling of the core extends, substantially, from the position where the introduction means discharges the core, up to the nip between the two winder rollers. To make the transit of the core from the non-moving surface or track to the second rotating winder roller easier, the surface is preferably comb-shaped, at least in the terminal portion thereof. This comb-like terminal portion cooperates with annular slots in the second winder roller to allow the core, having the first turns of web material wound thereon, to be transferred smoothly and without shocks or strains to the nip between the winder rollers.
In practice, since the extension of the track surface on which the core rolls (prior to the insertion thereof into the nip) is relatively short, and the web material very thin, any increase in diameter due to the winding of the first turns is insignificant. Accordingly, the track or fixed surface can define, together with the cylindrical surface of the first winder roller, a channel of substantially uniform cross-section and, advantageously, of a height slightly lower than the diameter of the core. The difference between the height of the channel and the diameter of the core causes the latter to be slightly squeezed when initially inserted thereinto, and this advantageously allows the web material to adhere to the core while facilitating the rotational acceleration of the core.
In practice, the severing means are so constructed as to be able to move along a cylindrical path which is almost tangent to the cylindrical surface of the first winder roller, or slightly interfering therewith. The peripheral speed of the cylindrical surface of the first winder roller and of the web material carried thereon is different than the tangential speed of the severing means along the path. In this way, when the web material is pinched between the severing means and the cylindrical surface of the first winder roller, the difference in speed causes a slight retardation of the web material and thus the tearing thereof. The rotational speed of the unit which carries the severing means is precisely controlled. Perforation lines on the web material adjacent the severing means will facilitate the tearing of the web material.
In order for the severing means to enter in contact with the web on the cylindrical surface of the first winder roller at an intermediate position along the channel, (while the rotary unit carrying the severing means is arranged outside the channel), the severing means pass through slots or apertures in the track. Thus, by controlling the rotational speed of the unit, the severing means moves out of the channel ahead of the core which is passing therethrough. The apertures or slots fin the track may be obtained, for example by providing a plurality of strips parallel to one another in the direction of advancement of the web material. The distance between the strips is sufficient to allow the passage of the severing means.
In order to increase the versatility of the machine and simplify the construction of the web material severing means, in a preferred embodiment of the rewinder, the severing means are made in the form of pressers or pads (resilient, if required) which press against the surface of the first winder roller, or other material feeding means, to pinch the web material. Advantageously, to make the tearing of the web material easier, in the regions where the pressers act against the roller, the surface of the first winder roller may have a low coefficient of friction. To this end, the first winder roller may be provided with a surface having wide annular bands suitably polished, having a low coefficient of friction, and separated by narrow annular strips having a high coefficient of friction. This ensures the proper friction on the web to properly feed the web, in particular at the moment when the new core is rotationally accelerated. The annular strips with high coefficient of friction may be aligned with the strips which define the track or core rolling surface.
With the arrangement above described, the length of the material wound into each individual log may be pre-determined and accurately controlled, regardless of the diameter or circumference of the first winder roller, inasmuch as there is no need for coordinating the position of the severing means with a particular portion of the surface of the winder roller, as is the case in the prior art machines.
Similar results in terms of versatility are attained if the severing means are provided with blade portions (saw-toothed, if required) which cooperate with annular channels in the first winder roller. Blade means could operate with a longitudinal slot instead of annular channels.
The unloading from the winder of a completed log or roll may take place by an accelerating third, diameter-control, roller disposed downstream of the first and second winder rollers, in a manner similar to that described in the above-mentioned GB-A-2,105,688. However, provision may also be made for the completed log to be unloaded by deceleration of the second winder roller, while keeping the peripheral speed of the third winder roller constant and substantially equal to the peripheral speed of the first winder roller. The deceleration of the second winder roller also causes the core to go through the nip defined by the first and second winder rollers.
It is not excluded that the core passes through the nip between the first and second winder rollers by means of a small and constant difference in the peripheral speed between the two winder rollers. In this case, it may be necessary to provide a relative mobility of the first and second winder rollers.
When provision is made for a deceleration of the second winder roller in order to unload the completed log and/or to allow the passage of the core through the nip, an actuator means may be provided which causes both the deceleration of the roller and the actuation of the web material severing means. This is possible because the latter will have to be operated only when a log has been completed and a new core has to be introduced, i.e., when the deceleration of the second winder roller is necessary. This greatly simplifies the structure of the machine.
With the above and other objects in view, further information and a better understanding of the present invention may be achieved by referring to the following detailed description.